Thermodynamic modelling of cements clinkering process as a tool for optimising the proportioning of raw meals containing alternative materials.

The valorisation of waste or by-products in Portland clinker production is a promising alternative for developing sustainable cements. The complexity of the chemical reactions during clinkering demands an adequate dosing method that considers the effect of feedstock impurities to maximise the potential substitution of natural resources by waste or by-products, while guaranteeing the clinker reactivity requirements. This study proposes a raw meal proportioning methodology for optimising co-processing of natural feedstocks with alternative raw materials in clinker production, intending to reduce the content of natural raw materials needed, while promoting an optimal clinker reactivity. A thermodynamic modelling sequence was developed considering the variability of raw materials composition and heating temperatures. The model was then validated by comparing simulation outcomes with results reported in previous studies. An experimental case study was conducted for validation of the proposed method using a spent fluid catalytic cracking catalyst (SFCC), a by-product from the oil industry as an alternative alumina source during clinkering. The modelling simulations indicated that substitution of natural feedstocks by 15 wt% SFCC promotes the formation of reactive clinkers with more than 54% tricalcium silicate (C3S). Mixes with the potential to form the highest C3S were then produced, and heating microscopy fusibility testing was applied for evaluating the clinkers' stability. The main factors governing the reactivity and stability of the clinker phases were the melt phase content, alumina modulus, and formation of C3S and dicalcium silicate (C2S). The self-pulverisation of clinker during cooling was observed in selected mixes, and it is potentially associated with high viscosity and low Fe content in the melt phase. The proposed framework enables optimisation of the dosing of raw meals containing alternative alumina-rich feedstocks for clinker production and allows a deeper interpretation of limited sets of empirical data.

Oil-based mud cutting as an additional raw material in clinker production.

Oil-Based Mud (OBM) cutting is a hazardous by-product generated during oil-well drilling. Its chemical composition suggests that it might be suitable as a raw material in cement manufacturing. It is rich in calcium oxide, silica, and aluminium oxide, which are the major oxides in raw materials for cement manufacturing. In this research, OBM cutting is used as a constituent of the raw meal for cement clinker production. Raw meal mixtures were prepared by mixing different ratios of raw materials increasing OBM content. The impact of the addition of OBM cutting on the resulting clinker has been investigated. The results demonstrate that OBM cutting could be recycled in the manufacturing of Portland cement clinker. Clinker prepared using OBM cutting had very similar properties to that prepared from limestone. This result could represent an opportunity for solving an environmental problem. The addition of OBM cutting lowers the calcination temperature, and increases the rate of carbonate dissociation. However, it also leads to a higher free lime in clinker, which is a result of the presence of trace elements, such as barium. Overall, its use as a raw material in cement production could provide a cost-effective, environment-friendly route for the management of OBM cutting.

Alkali activated solidification/stabilisation of air pollution control residues and co-fired pulverised fuel ash.

This paper examines the potential treatment by solidification/stabilisation (S/S) of air pollution control (APC) residues using only waste materials otherwise bound for disposal, namely a pulverised fuel ash (PFA) from a co-fired power station and a waste caustic solution. The use of waste materials to stabilise hazardous wastes in order to meet waste acceptance criteria (WAC) would offer an economical and efficient method for reducing the environmental impact of the hazardous waste. The potential is examined against leach limits for chlorides, sulphates and total dissolved solids, and compressive strength performance described in the WAC for stable non-reactive (SNR) hazardous waste landfill cells in England and Wales. The work demonstrates some potential for the treatment, including suitable compressive strengths to meet regulatory limits. Monolithic leach results showed good encapsulation compared to previous work using a more traditional cement binder. However, consistent with previous work, SNR WAC for chlorides was not met, suggesting the need for a washing stage. The potential problems of using a non-EN450 PFA for S/S applications were also highlighted, as well as experimental results which demonstrate the effect of ionic interactions on the mobility of phases during regulatory leach testing.

Preparation of nanostructured materials by heterocoagulation-interaction of montmorillonite with synthetic hematite particles.

A nanostructured, porous material was prepared by heterocoagulation of negatively charged montmorillonite with positively charged synthetic spherical hematite particles. The process of heterocoagulation of such particles was monitored by turbidimetric titrations over the pH range 2.5-7.5. On the basis of the results of turbidimetric measurements, a series of solid materials were prepared for further characterization using ESEM, BET, XRD, and FTIR techniques. Environmental scanning electron microscopy detected isolated hematite particles or small hematite aggregates on montmorillonite surfaces (mass ratios 8:1 and 4:1). At a mass ratio of 1:1, exfoliated montmorillonite layers, covering the hematite particles as semi-transparent blankets were seen. A low mass ratio led to compact hematite particle aggregates covering the montmorillonite surfaces. Nitrogen-gas-adsorption isotherms revealed the sorption properties to be gradually dependent upon mass ratios. Pore volume distributions showed that mesopores with diameter of about 10-20 nm were produced in the heterocoagulates with mass ratios of 4:1, 1:1, and 1:8. The sample prepared with a 4:1 mass ratio showed the greatest BET surface area, which decreased slightly upon sample calcination at 500 degrees C. X-ray diffraction measurements were used to investigate layer stacking, by comparing the integral intensities of d(001) reflection. For this purpose, samples with 4:1 mass ratios, prepared both by heterocoagulation and mechanical grinding, were used. It was found that heterocoagulation effectively diminished the stacking of the layers to about 85%; hence, a significant amount of fundamental, 1 nm thick montmorillonite layers was achieved in this sample.